The present invention concerns a photometer for performing measurements at various wavelengths and which allows measurements to be made after a short warm up period, thus increasing the throughput of the system and extending the useable lifetime of the light source. The system also allows resonant frequency mixing of the sample for increasing the throughput of the system and the accuracy of the measurements.
Photometers have been used for performing analysis of various analytes. In one application, a reagent tablet and diluent are inserted into a cuvette and mixed until the reagent tablet dissolves in the diluent. The mixing may be done with a stirring rod inserted into the cuvette, or by oscillating the cuvette in an off line shaker. The sample to be analyzed, such as blood serum, is then added to the cuvette and again mixed. After the contents are added to the cuvette it is often desirable to warm the contents to a highly precise temperature. The mixing action promotes highly effective heat transfer between the heater surrounding the cuvette and the cuvette contents so that the temperature of the contents achieves stability much more quickly. The cuvette is then inserted into a holder within the photometer and a photometric analysis of the reaction product is performed.
Some of the principle disadvantages of known photometers are the extended warm up period required to stabilize the output of the light source before a measurement can be taken and the short lifetime of the lamp bulb. Furthermore, off-line mixing of the cuvette contents requires additional handling by the operator and is inefficient--i.e., it allows the contents of the cuvette to cool during transfer from the mixing instrument to the measuring instrument and allows partial settlement before a measurement can be taken.
For example, a problem with the prior art tungsten filament bulb in applications requiring a measurement near the ultraviolet spectrum is that the filament is required to run at temperatures above 2900.degree. K. This high temperature limits the life of the bulb due to evaporation of tungsten from the filament and its deposition on the inner surface of the bulb. The filament is weakened by this evaporation and as the bulb is blackened, less light is emitted from the bulb.
One prior art solution has been to utilize a tungsten filament bulb filled with halogen gas e.g., bromine or iodine. A chemical reaction between the tungsten and halogen removes the tungsten from the surface of the bulb and redeposits it on the filament. This increases the life of the bulb. However, a disadvantage is that the bulb must be on for at least fifteen minutes to bring it up to full temperature (bulb temperature of 250.degree. C.) for the halogen redeposition to take place. Still further, the emitted light intensity does not stabilize until the bulb is fully warmed and stable, typically about 15-30 minutes. Thus, the halogen bulb is generally left on for long periods of time between measurements, resulting in a reduced useful bulb life.
It is an object of this invention to provide a photometer capable of performing chemical and immunochemical assays on a broad array of analytes.
Another object is to provide the fastest possible warm up of the cuvette contents to a highly precise temperature.
A further object is to provide a photometer which allows measurements to be taken after a short warm up period, thus allowing the light source to be turned off between measurements and extending the useful lifetime of the source.
A still further object is to provide a photometer which provides vigorous mixing of the contents of the cuvette and which allows ready determination of the optimum mixing frequency.